The present invention relates to extrusion methods, in particular for shaping polymer solutions or polymer fluids.
Cellulose and other polymers can be dissolved in suitable solvents and transferred by controlled solidification into a desired shaped article. If this shaped article is constituted by fibres, fibrils and the like, reference is also made to a spinning process. Cellulose is dissolved for example in aqueous solutions of amine oxides, in particular solutions of N-methylmorpholine N-oxide (NMMO), in order to produce spinning products, such as filaments, staple fibres, films, etc., from the obtained spinning solution. This occurs by precipitation of the extrudates in the water or diluted amine oxide solutions once the extrudates of the extrusion die are guided via an air gap into the precipitation bath.
U.S. Pat. No. 4,416,698 relates to an extrusion or spinning method for cellulose solutions in order to shape cellulose into fibres. In this case, a fluid spinning material—a solution of cellulose and NMMO (N-methylmorpholine N-oxide) or other tertiary amines—is shaped by extrusion and brought into a precipitation bath for solidification and expansion. This method is also known as the “lyocell” method.
U.S. Pat. No. 4,246,221 and DE 2913589 describe methods for producing cellulose filaments or films, wherein the cellulose is drawn in fluid form. These documents describe a spinning process in which cellulose is dissolved in tertiary amine oxide, wherein the obtained cellulose solution is pressed via a die, is extruded via an air gap into a spinning funnel, and is discharged at the end of the spinning funnel in the form of continuous fibre. The spinning funnel used is equipped with a feed means and a discharge means for the spinning bath.
A further method is described in U.S. Pat. No. 5,252,284, in which elongate shaping capillaries are used to shape a cellulose material.
WO 93/19230 A1 describes a further development of the lyocell method, in which the cellulose-containing spinning material is cooled immediately after the shaping process before introduction into the precipitation bath.
WO 94/28218 A1 describes a method for producing cellulose filaments, in which a cellulose solution is shaped into a number of strands via a die. These strands are introduced into a precipitation bath (“spinning bath”) through a gap around which gas flows and are discharged continuously.
A shaping device and a further variant of the lyocell method are described in WO 03/057951, wherein the cellulose-containing spinning material, after shaping, is conveyed via a shielding region and then via a cooling region.
In EP 0 430 926 B1, a spinneret with a spinneret head and a spinning plate is presented, wherein the spinning plate consists of a stable carrier plate provided with bores. Spinneret plates, in which spinning capillaries are formed, are inserted into the aforementioned bores.
U.S. Pat. No. 5,951,932 A relates to a method for producing lyocell fibres with the known steps of extrusion of the cellulose fibres, passing of said fibres through an air gap with an airflow, and introduction into a precipitation bath. A range from 95° C. to 125° C. is mentioned as a possible temperature in the spinning cell. The extrusion pressure of some embodiments is to be between 20 and 100 bar. A pressure difference between the spinning material and the pressure in the air gap is not described. In addition, there is no information concerning the pressure and temperature at which extrusion is to be performed.
U.S. Pat. No. 5,417,909 A is a further document that describes a lyocell method. Temperatures between 70° C. and 115° C. are specified in examples 6 to 12. Lower spinning temperatures will demonstrate improved spinning behaviour. There is no information concerning pressure.
U.S. 2005/220916 A1 describes a lyocell spinning method with spinning temperatures between 80° C. and 102° C. No information concerning pressure is provided however.
DE 100 43 297 A1 specifies a spinning temperature of 85° C., but does not specify pressure.
The publication “The Temperature of Fibres during Air-Gap Wet Spinning: Cooling by Convection and Evaporation”—Volker Simon (Int. J. Heat Mass Transfer. Vol. 37, No. 7, pp. 1133-1142, 1994) presents courses of events in the spinning process. It is stated that the polymer material fed into the air gap contains water and that the water evaporates at the surface of the spinning fibre during the spinning process and this water evaporation has a cooling effect on the spinning fibre. It is concluded that the fibre temperature during extrusion is relatively high and the water concentration in the spinning environment is increased by the evaporation of the water from the fibre.
It is specified that the result is that the water vapour gradient causes the water vapour mass flow to be guided from the fibre in the direction of the surrounding environment. The water evaporation taking place in the filament is enabled by the quantity of water located in the filament, whereby a strong cooling effect, greater than with melt spinning, is produced. In a further statement, it is mentioned that the spinning material used in the NMMO method consists of a non-solvent (water), a solvent (amine oxide=NMMO) and cellulose. The author ultimately comes to the conclusion that the solvent does not evaporate during the shaping process.